(a) Field of the Invention
The present invention relates to a preparation method of a superabsorbent polymer, and specifically to a method of preparing a superabsorbent polymer of which fine powder generation is small, and not only are water holding capacity and absorbing power under pressure excellent, but also the content of a water soluble component is low.
(b) Description of the Related Art
A superabsorbent polymer (SAP) is a synthetic polymer material having a function of absorbing about 500 to about 1000 times its weight of water, and it has been differently called a superabsorbency material (SAM), an absorbent gel material (AGM), and so on by developing enterprises. The superabsorbent polymer disclosed above started to be commercialized for sanitary items, and is now being used widely as a water combination soil for horticulture, a water-stop material for civil engineering and construction, a nursery sheet, a freshness preservative in the food distribution field, a poultice material, and the like in addition to the sanitary fittings like a paper diaper for a child.
An inverse suspension polymerization method or an aqueous polymerization method is known as a method of preparing a superabsorbent polymer. For example, inverse suspension polymerization is disclosed in Japanese Patent Publication Nos. Sho56-161408, Sho57-158209, Sho57-198714, and so on. As the aqueous polymerization method, a thermal polymerization method of polymerizing a hydrous gel phase polymer while fracturing and cooling the same in a kneader equipped with a plurality of spindles, and a photo-polymerization method of exposing a high-concentrated aqueous solution on a belt to UV rays and the like so as to carry out the polymerization and dry it at the same time are known.
Meanwhile, a polymer powder obtained from the processes of polymerization, pulverization, drying, and final milling is surface treated for obtaining a hydrous gel phase polymer having excellent properties, and various modifications of the processes have been attempted for increasing the effects of the steps of polymerization, pulverization, and drying in order to obtain a hydrous gel phase polymer having excellent properties.